1-Stage Freedom analysis

Calculate cluster-level sensitivity and specificity for range of sample sizes and cut-points for given cluster size and imperfect tests

Test sensitivity

Test specificity

Cluster size

Sample size range:

From

To

Step

Design prevalence values (enter up to 5 values, as proportions):

1

2

3

4

5

Cut-point range:

From

To

Method of calculation

Binomial HerdPlus HerdAcc FreeCalc

Precision (significant digits)

Submit

This utility calculates cluster sensitivity (SeH) and cluster specificity (SpH) for a range of sample sizes and cut-point numbers of reactors, for specified cluster size, test sensitivity, test specificity and design prevalence values. Options for calculations include four different estimation methods:

• Binomial distribution: where cluster size is not specified;
• HerdPlus: Using the hypergeometric distribution;
• HerdAcc: Jordan D, McEwen SA, 1998. Herd-level test performance based on uncertain estimates of individual test performance, individual true prevalence and herd true prevalence. Prev. Vet. Med. 3: 187-209; and
• FreeCalc: Cameron AR, Baldock FC, 1998. A new probability formula for surveys to substantiate freedom from disease. Prev. Vet. Med. 34: 1-17.

Inputs include:

• Test sensitivity and specificity;
• Specified cluster/population size;
• Maximum and minimum sample sizes to be considered and the step in values;
• Up to 5 unit-level design prevalences (the hypothetical prevalence to be detected, as proportions);
• Maximum and minimum cut-point number of positives to classify a cluster (herd/flock) as positive;
• The preferred calculation method; and
• The desired precision of results (number of digits to be displayed after the decimal point).

Outputs include:

• Tables and plots of SeH and SpH for each design prevalence value for combinations of sample size and cut-points; and
• An excel file of the results.